Disk drives, also called disk files, are information storage devices that use a rotatable disk with concentric data tracks containing the information, a head or transducer for reading and/or writing data onto the various tracks, and an actuator connected to a carrier for the head for moving the head to the desired track and maintaining it over the track centerline during read or write operations. There are typically a plurality of disks separated by spacer rings and stacked on a hub that is rotated by a disk drive motor. A housing supports the drive motor and head actuator and surrounds the head and disk to provide a substantially sealed environment for the head-disk interface.
In conventional magnetic recording disk drives, the head carrier is an air-bearing slider that rides on a bearing of air above the disk surface when the disk is rotating at its operational speed. The slider is maintained next to the disk surface by a relatively fragile suspension that connects the slider to a rotary actuator. The slider is either biased toward the disk surface by a small spring force from the suspension, or is "self-loaded" to the disk surface by means of a "negative-pressure" air-bearing surface on the slider.
To improve the wear resistance of the disk, as well as to maintain consistent magnetic properties, it is desirable to make the disk surface as smooth as possible. However, a very smooth disk surface creates a problem known as "stiction". This means that after the slider has been in stationary contact with the disk for a period of time, the slider tends to resist translational movement or "stick" to the disk surface. Stiction is caused by a variety of factors, including static friction and adhesion forces between the disk and slider created by the lubricant on the disk. Stiction in a disk drive can result in damage to the head, disk, or suspension when the slider suddenly breaks free from the disk surface when disk rotation is initiated. In some disk drives, such as low-power disk drives used in laptop and notebook computers, the drive motor may simply be unable to initiate rotation or achieve operating speed because of the adhesion forces that cause stuck sliders or excessive drag.
To prevent the problem of stiction that occurs if the slider comes to rest on the disk surface, conventional disk drives park the actuator against one of its two "crash stops" so that the slider is maintained away from the data region of the disk when the drive is not operating. Contact start/stop (CSS) disk drives, i.e., those that operate with the slider in contact with the disk surface during start and stop operations, use a dedicated landing zone where the slider is parked when the drive is not operating. Typically, the landing zone is a specially textured nondata region near the inside diameter (ID) of the disk. In contrast to CSS disk drives, "load/unload" disk drives address the stiction problem by mechanically unloading the slider from the disk when the power is turned off, and then loading the slider back to the disk when the disk has reached a speed sufficient to generate the air bearing. The loading and unloading is typically done by means of a ramp that contacts the suspension when the actuator is moved away from the data region of the disk. The slider is thus parked off the disk surface with the suspension supported in a recess of the ramp.
A separate reason for parking the actuator when the disk drive is not operating is that the head, disk, or suspension can be damaged by a sudden external force that drives the slider onto the disk. This is especially likely in laptop computers.
In contrast to conventional air-beating disk drives, contact or near-contact disk drives have been proposed that place the head carrier in constant or occasional contact with the disk or a liquid film on the disk during read and write operations. Examples of these types of disk drives are described in IBM's U.S. Pat. No. 5,202,803 and published European application EP 367510; U.S. Pat. No. 5,097,368 assigned to Conner Peripherals; and U.S. Pat. No. 5,041,932 assigned to Censtor Corporation. These types of disk drives may also be of the type that park the actuator with the head carrier away from the data region of the disk when the drive is not operating.
Because of the adverse consequences if the head carrier contacts or impacts the data region of the disk, disk drives that park the actuator typically have some type of actuator lock to prevent the actuator from moving the carrier toward the data region of the disk in the event of an external shock. Passive magnetic or spring locks apply restraining forces that are overcome when the drive is turned on and the actuator is activated. Solenoid locks engage the actuator when power is off and release when a current pulse is applied. A rotary inertial lock, as described in U.S. Pat. No. 5,189,576 assigned to Integral Peripherals, locks the rotary actuator in the presence of an external force that causes the parked actuator to move away from its crash stop toward the data region of the disk. The passive locks are especially subject to failure in the presence of a sudden external force, the solenoid locks are unreliable, and the inertial rotary lock has been found to be inoperable in the presence of an external force that causes the parked actuator to move into its crash stop.
What is needed is a disk drive with a reliable lock for the parked rotary actuator that operates regardless of the direction of the external force.